Traditional airfield lighting products, such as taxiway lights, comprise a light source enclosed in an optical element that directs the light into an appropriate beam while protecting the light source from the environment.
The traditional optical element is usually a Fresnel optic designed to create a substantially horizontal fan beam. Traditional airfield lights using LEDs are illustrated in U.S. Pat. Nos. 7,192,155 and 6,425,678 and in FIG. 1. The horizontal fan beam, extending between the horizon and about 10° above the horizon, is directed at air traffic. Because the optical element is clear on top, a substantial amount of light shines upwards, to angles between 10° and 90° from the horizon.
In fact, high angle light is required by the Federal Aviation Administration (FAA) for taxiway lights as set out in FAA Advisory Circular (AC) 150/5345-46c, under the designation L-861T. Additionally, high angle light is often needed from runway edge lights as well. While such requirement is not part of FAA requirements, the International Civil Aviation Organization (ICAO) requires light at high angles when the runway edge lights lights are to be used for circling guidance.
Solar powered LED airfield lights, as illustrated in FIG. 2, are becoming increasingly accepted as an alternative to traditional electrical grid-powered lights. Like traditional lights, they often use a Fresnel lens. However, unlike the traditional lights, they often have a solar panel on the top. The panel is opaque and overhangs the optical element thereby limiting the amount of light that can be directed upwards to high angles, as illustrated for example in U.S. Pat. No. 6,013,985. It is thought that this is one of the reasons that the FAA has thus far been reluctant to approve solar-powered airfield lights.
It is therefore an object of the present invention to provide an airfield light that is solar-powered, having a solar panel covering the top of the light, and that nonetheless provides high angle light to comply with high angle light requirements for taxiway and runway edge lights.
This and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows.